1. Field of the Invention
The invention relates to a vehicle with hybrid drive, in which the driving power provided by an internal combustion engine or an electric motor is fed to the drive train via a transmission with a transmission input shaft and a transmission output shaft. The internal combustion engine and the electric motor are connectable to each other via a coupling. The electric motor is directly connected to the transmission. The vehicle also includes an electric energy storage device for providing power to the electric motor that is chargeable by the internal combustion engine. A process for operating a hybrid vehicle with a satellite-controlled navigation system is also disclosed.
2. Description of the Related Art
A hybrid vehicle of the aforementioned type is known, for example, from references DE 43 23 601 A1 and DE 29 43 554. The reference DE 29 43 554 discloses a hybrid vehicle started by the electric motor alone. The internal combustion engine (ICE) of this prior art vehicle is started only after a minimum speed is attained using the stored kinetic energy of rotating masses between two separating couplings. After being started, the ICE is accelerated very quickly to the speed of the electric motor. During uphill and/or accelerating travel, the electric motor is operated with the ICE, in a known manner, as a simultaneously acting driving engine, and during downhill and/or deceleration phases, the electric motor is operated as a generator to feed an energy storage device.
Another prior art reference DE 44 22 636 A1 discloses a process for the automatic control of an ICE in hybrid vehicles. This prior art control process discloses using one of four operating modes of the ICE depending on the driving state of the vehicle. In a first operating mode, power is provided by the ICE only when a preestablished minimum value of an operating parameter proportional to the vehicle speed is reached. In a second operating mode, power is provided by the ICE when the total power demanded exceeds a short-term power limit. In a third operating mode, power is provided by the ICE delayed by a preestablished time period when the total power demanded exceeds a long-term power limit and falls below a short-term power limit. In a fourth operating mode, when the charge level of the electric energy storage device has dropped to a lower limit, power is provided by the ICE until an upper limit of the charge level is again attained. The ICE is turned on when the power available from the electric motor is no longer sufficient. The long-term power limit is defined in the aforementioned publication as the power that can be delivered permanently by the electric energy storage device.
Yet another control device for a hybrid vehicle is disclosed in prior art reference DE 195 23 985 A1. In this control device, power produced by the driving engine is applied via a generator inverter to an engine/generator, so that the engine/generator drives the ICE to apply a braking force to the latter. In this way, power produced during regenerative braking that cannot be absorbed by a saturated battery (such as during downhill travel) is used to support the braking of the vehicle.
All known hybrid vehicles require a large structural space for the driving unit because the ICE and the electric motor are connected one behind the other with a coupling between them and the transmission is connected to the electric motor. The additional space requirement created by the parallel hybrid drive must be as small as possible. For installation in existing vehicles having a conventional drive unit, a maximum lengthening of 30 mm, compared with the conventional driving unit, is permissible. Otherwise, the structure of the vehicle would have to be modified. Given the low production number of the hybrid vehicles, any required structural modification would lead to a considerably greater expense. Therefore a problem of the prior art hybrid vehicles is to minimize the additional space requirement. In addition, the use of each of the ICE and electric motor must be properly selected to produce the greatest savings in fuel consumption.
To solve the problems of the prior art, a generic vehicle according to the present invention includes a hybrid drive in which the torque that is provided by the electric motor is greater than the maximum torque of the internal combustion engine. In addition, the transmission input shaft and the transmission output shaft always turn in the same forward rotation direction when driven by the ICE. Reverse travel is possible exclusively via the electric motor.
Instead of low-torque motors, an electric motor with a substantially higher torque than the internal combustion engine is used at low speeds. The axial structural space required by this higher torque electric motor is compensated for by a space-saving transmission, which omits a reverse gear. The forward rotational direction of the transmission input shaft and output shaft can not be changed during operation by the ICE. With the higher torque electric motor, it is possible to start movement of a vehicle using a gear that is normally used as a second gear with conventional motors. Omitting the reverse gear allows the axial structural space of the transmission to be reduced. The additional omission of the conventional first gear leads to a further reduction of the structural space of the transmission. The high torque of the electric motor, which is preferably an external rotor motor, may also be used for applying a braking force to the vehicle.
The ICE and the electric motor are preferably connectable in series so that both the ICE and the electric motor can provide power simultaneously when a driving power required by the vehicle is greater than that which can be provided by one of the ICE and electric motor alone.
Preferably, braking is brought about by switching the electric motor to generator operation. The braking energy may then be taken from the electric storage device as required to brake the vehicle.
When the vehicle is equipped with a satellite-controlled navigation system such as a global positioning system (GPS), operation of the vehicle may be controlled in a preplanned manner. In an especially advantageous embodiment, the navigation system or a computer arranged with the navigation system includes or receives elevational or topographical data on at least some of the routes within a given region.
A process for operating the above-described vehicle with a GPS according to an embodiment of the invention includes the following steps:
inputting current vehicle parameters including fuel supply and charge level of electric energy storage device and of additional charge into a computer connected to the navigation system;
inputting a desired destination into the computer;
calculating an expected travel time in response to the route topography and assuming the uniform use of the ICE and the electric motor and displaying the calculated expected travel time on a display device;
comparing the expected travel time with a travel time predetermined by the driver and recalculating the expected travel time using different amounts of use of the ICE and the electric motor if required;
adjusting a respective use of the ICE and the electric motor to the route to realize the desired travel time, before starting the trip; and
establishing charging cycles for charging the energy storage device by the ICE, along the route excluding the periods of downhill travel by the vehicle.
In designing the hybrid vehicle according to the present invention, it is assumed that from the total quantity of fuel used, for example, 4.6 liter/100 km, given a vehicle weight of 1 ton and 500 kg maximum additional load, the ICE produces approximately 30% mechanical power and 70% waste heat. Regarding the mechanical power produced by the ICE, ⅕ is used for each of overcoming friction, maintaining speed and acceleration, while approximately {fraction (1/10)} is used for the auxiliary output. Regarding the waste heat produced by the ICE, 40% is lost as heat in the cooling circuit and must be extracted. Of this lost heat in the cooling circuit, 10% can be used for heating and 30% is discharged in the exhaust gas. Since 10% of the waste heat is useable, the total loss of the mechanical power equals 60%. In a hybrid vehicle, this total loss can be halved, as can 10% of the power used for acceleration. By using a recuperative arrangement in a hybrid vehicle, 50% of the energy wasted by a conventional ICE is recoverable, so that the hybrid vehicle uses approximately 35% less energy than a conventional ICE alone uses. The goal of the hybrid vehicles is to consume, instead of 4.6 liters, only 3 liters per 100 km.
To attain energy savings with a hybrid vehicle with the same total weight as a comparable conventional vehicle, an electric energy storage device that is chargeable by the internal combustion engine should be used, for example. Moreover, electric auxiliary outputs should be designed so as to relieve the internal combustion engine at least at times. Instead of a long-term battery, it is desirable that the electric energy storage device include a fuel cell
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of the disclosure. For a better understanding of the invention, its operating advantages, and specific objects attained by its use, reference should be had to the drawing and descriptive matter in which there are illustrated and described preferred embodiments of the invention.